if you need to notify by error group/message, you will need dedicated watches for each of those group in order to have throttling up and running, there is no way around that.

If you do not know them in advance, it might make sense to have some generic catch all watch (that alerts all the time) and then add new watches, if you know the message over time.

Another idea might be to always alert on all messages, but implement the throttling yourself in the script condition (because this is custom logic) so you decide for example based on the last 5 runs (which are stored in the watch history and can be queried using a chained input), if something should be triggered or not.

Another current limitation is the fact, that you can only send out a single email per watch, you cannot send a dedicated email per message log type or something.